1. Field of the Invention
The present invention relates to an optical disk drive (for example, compact disk drive or DVD drive) capable of reading data stored on an optical disk (for example, CD or DVD). More specifically, the present invention discloses an optical disk drive comprising an adaptive compensator for preventing an actuator from entering a non-linear region.
2. Description of the Prior Art
In current technology, an optical disk is lightweight, small physical volume, and low cost. In addition, optical disks have a high capacity for information storage, making optical disks an indispensable information-storing medium.
Of course, high-density information stored on an optical disk is read out by an optical disk drive for further processing. The high-speed requirements of modern society demand not only a continuous increase of data storage density on the optical disk, but also demand a high speed optical disk drive for reading the data on the optical disk. In order to allow the optical disk drive to read high-density data quickly, the optical disk drive must have a precise control system. Therefore, developing a precise control system for the optical disk drive is an important topic of the information industry.
Please refer to FIG. 1. FIG. 1 is a perspective view of an optical disk drive 10 according to the prior art. The optical disk drive 10 reads data stored on an optical disk 14. The optical disk drive 10 includes a housing 12 and a rotatable base 16 installed on the housing 12. The housing 12 further comprises a hole 17 that shows a sled 18 inside the housing 12. The sled 18 inside the housing 12 is capable of sliding left and right so as to scan data stored on the optical disk 14. When the optical disk 14 is put on the base 16 and rotated by the base 16, the sled 18 slides left and right along the hole 17 so that the optical disk drive 10 reads data stored on the optical disk 14.
For further illustration of the inner construction of the optical disk drive 10, please refer to FIG. 2. FIG. 2 is a perspective view of the inner structure of the optical disk drive 10 according to the prior art. In order to clearly show the inner structure of the optical disk drive 10, a portion of the housing 12 of the optical disk drive 10 is omitted in FIG. 2. Inside the optical disk drive 10, a spindle motor 15 on the housing 12 is capable of rotating the base 16 and further driving the optical disk 14 on the base 16. For clarity, FIG. 2 only shows a portion of the optical disk 14. The sled 18 slides left and right on a path 30 along a direction 34 shown in FIG. 2. The sliding of the sled 18 is driven by a driving device 20. The driving device 20 comprises a driving motor 20a installed inside the housing 12, a gear 20b rotated by the driving motor 20a and a saw tooth plate 20c on the sled 18. When the driving motor 20a rotates the gear 20b, the saw tooth plate 20c, engaging with the gear 20b, pushes the sled 18 to slide left and right along the slide 30. For reading high-density data stored on the optical disk 14, the sled 18 controls an actuator 22, which is capable of moving left and right in a direction 36 within a predetermined range on the sled 18, as shown in FIG. 2. A lens 32 is installed on the actuator 22, and connects with a light source 26 installed on the sled 18. Light (for example, a laser) is emitted from the light source 26 and passes through the lens 32 on the actuator 22 optically, and then shines on the bottom surface of the optical disk 14. The light reflected from the optical disk 14 passes through the lens 32 on the actuator 22. The light is then sent back to the sled 18, so that the optical disk drive 10 is capable of reading the data stored on the optical disk 14. Meanwhile, the actuator 22 slides left and right on the sled 18, and is driven by a servo device 24 on the sled 18. The servo device 24 provides a push force to drive the actuator 22 left and right.
In order to read the high-density data stored on the optical disk 14 well, the optical disk drive 10 comprises a control system for controlling the operation of the actuator 22 and the sled 18. Please refer to FIG. 3. FIG. 3 is a diagram of the control system of the optical disk drive 10 according to the prior art. In the current optical disk standard, data is written onto the optical disk 14 along tracks. The optical disk shown in FIG. 3 shows one of the tracks 46 with data stored therein. For reading data on the track 46, the sled 18 and the actuator 22 on the optical disk drive 10 must make the lens 32 lock the position of the track 46. Therefore, the optical disk drive 10 is capable of reading data stored on the track 46 with the rotation of the optical disk 14. For this purpose, the control system of the optical disk drive 10 comprises a control circuitry 38 for controlling the operation of the optical disk drive 10. The control circuitry 38 has a compensation device 48 for controlling both the driving device 20 and the servo device 24. Furthermore, a sensor 28 is installed on the sled 18 and is connected with the actuator 22. This means that the light emitted from the light source 26 passes through the lens 32 and shines incident onto the optical disk 14. The light may be reflected from the optical disk 14 into the sensor 28 by passing through the lens 32 on the actuator 22 again. By analyzing the light incident on the sensor 28, the sensor 28 is capable of sensing whether the lens 32 locks on the track 46. The result is then transmitted into the control circuitry 38. According to this result, the control circuitry 38 makes the compensation device 48 to control the driving device 20 and the servo device 24 for adjusting the operation of the sled 18 and the actuator 22 respectively. Therefore, the lens 32 is able to lock the track 46, and the optical disk drive 10 reads data stored on the track 46 of the optical disk 14 correctly.
The control system of the prior optical disk drive 10 is used for locking the track 46. The control circuitry 38 controls the operation of the sled 18 and the actuator 22 through the driving device 20 and the servo device 24 respectively. Compared with the actuator 22, the move range of the sled 18 is larger, but the response of the control circuitry 38 is slower. In addition, the movement of the sled 18 is not very accurate, so it can only make a rough locking motion. On the other hand, the move range of the actuator 22 is smaller, but the response is quicker. So the actuator 22 is able to make an accurate locking. The control circuitry 38 controls both the sled 18 and the actuator 22, so the control circuitry 38 needs to give consideration to both kinds of track locking. The control of the sled 18 and the actuator 22 is not only related with the control circuitry 38, but also related with the mechanical characteristics of the driving device 20 and the servo device 24. Please refer to FIG. 3 again. The servo device 24 provides a pushing force to push the actuator 22 left and right within a predetermined range 40 on the sled 18, but the relationship between the push force received by the actuator 22 and the displacement of the actuator 22 within the predetermined range may change due to different positions of the actuator 22 in the predetermined range. The predetermined range 40 is divided into a linear region 44 and a non-linear region 42. In the linear region 44, the push force, provided by the servo device 24 for pushing the actuator 22, has a linear relationship with the displacement of the actuator 22. Relatively, within the non-linear region 42 of the predetermined range 40, the push force received by the actuator 22 has a non-linear relationship with the displacement of the actuator 22.
In the linear region 44, the control circuitry 38 provides a push force to the actuator 22 through the servo device 24. This push force controls the position of the actuator on the sled 18 and keeps the linear relation between the sled 18 and the actuator 22. Alternatively, in the non-linear region 42, the control circuitry 38 22 would be unable to control and the position of the actuator 22 on the servo device 24 is unknown. Thus, the control circuitry 38 would be unable to keep the relation of the sled 18 and the actuator 22 in the non-linear region 42. Once the relation between the sled 18 and the actuator 22 is unknown, the optical disk drive 10 may be unable to lock the track 46 and read data stored on the optical disk 14 correctly. When designing the compensation device 48 of the control circuitry 38, designers may specially set the relation between the sled 18 and the actuator 22 so as to keep the position of the actuator 22 within the linear region 44 of the predetermined range 40.
In modern industry, there are many components inside an optical disk drive. The driving device 20, the sled 18, the servo device 24, the actuator 22, and the control circuitry 38 may be from different vendors. The design of the compensation device 48 had better according to the specifications of the hardware device. However, there may be some inevitable errors during production, and the produced hardware device may be some different from the specifications of the original design. Although the compensation device 48 of the control circuitry 38 is designed according to the specifications of the hardware device so as to keep the actuator 22 inside the linear region 44 on the sled 18, there may be some negative effects on the set relation control in the compensation device 48. Therefore, the optical disk drive 10 may be unable to lock the track 46 fast and correctly. Of course, a poor design of the compensation device 48 also deteriorates the relationship, and lets the actuator 22 enter the non-linear region 42, making the actuator 22 difficult to control. Further, the deviation phenomenon caused by poor manufacturing of the optical disk 14 can also deteriorate the relationship. The run-out phenomenon of the optical disk 14 is caused when the rotation axis of the base 16 and the center of the circular optical disk 14 do not match. Ultimately, the run-out phenomenon makes the position of the track 46 on the optical disk 14 unpredictable. In the optical disk drive with high access rate, the rotation speed of the optical disk 14 is especially high, so that the negative effect on tracking caused by the run-out phenomenon is obvious. In this case, the rotation of the track 46 is not circular when the optical disk 14 rotates. Therefore, the sled 18 and the actuator 22 also need to change position quickly so as to lock the track 46. If the control response of the relation is too slow, then the actuator may unexpectedly enter into the non-linear region.